Cellular communication systems continue to grow in popularity and have become an integral part of both personal and business communications. Cellular telephones allow users to place and receive phone calls most anywhere they travel. Moreover, as cellular telephone technology is increased, so too has the functionality of cellular devices. For example, many cellular devices now incorporate Personal Digital Assistant (PDA) features such as calendars, address books, task lists, calculators, memo and writing programs, etc. These multi-function devices usually allow users to wirelessly send and receive electronic mail (email) messages and access the internet via a cellular network and/or a wireless local area network (WLAN), for example.
As the functionality of cellular communications devices continues to increase, so too does demand for smaller devices that are easier and more convenient for users to carry. Nevertheless, the move towards multi-functional devices makes miniaturization more difficult as the requisite number of installed components increases. Indeed, the typical cellular communications may include several antennas, for example, a cellular antenna, a global positioning antenna, and a WiFi IEEE 802.11g antenna. These antennas may comprise external antennas and internal antennas.
Generally speaking, internal antennas allow cell phones to have a smaller footprint than external antennas. Moreover, they are also are preferred over external antennas for mechanical and ergonomic reasons. Internal antennas are also protected by the mobile device housing and therefore tend to be more durable than external antennas. External antennas may be cumbersome and may make the mobile device difficult to use, particularly in limited-space environments. Yet, one potential drawback of typical internal cellular phone antennas is that they are in relatively close proximity to the user's head when the phone is in use. As an antenna moves closer to a user's body, the amount of radio frequency (RF) energy radiation absorbed by the body will typically increase. The amount of RF energy absorbed by a body when using a mobile phone is called the specific absorption rate (SAR), and the allowable SAR for mobile phones is typically limited by applicable government regulations to ensure safe user RF energy exposure levels.